Tag Archives: association scheme

Proper Jordan schemes exist!

Posted on 28/06/2019 by Peter Cameron

A new field of research has just been created by Misha Klin, Misha Muzychuk and Sven Reichard: proper Jordan schemes. They answered a question which I posed some time ago (I don’t remember when), about whether such objects exist. I … Continue reading →

Posted in exposition | Tagged , , , , , , , | 1 Comment

Association schemes for diagonal groups

Posted on 12/05/2019 by Peter Cameron

Sean Eberhard commented on my posts on diagonal groups (see here and here). He is correct; there is an association scheme preserved by the full diagonal group with n factors in the socle; it is non-trivial if n > 2. The details … Continue reading →

Posted in open problems | Tagged , , , | 1 Comment

A problem

Posted on 07/12/2017 by Peter Cameron

Since I have been saying rather a lot about association schemes and coherent configurations lately, I thought I would mention an open problem. This is probably one for the experts, and I guess it has been ignored because of the … Continue reading →

Posted in open problems | Tagged , , | 8 Comments

Synchronization and all that, 2

Posted on 10/10/2017 by Peter Cameron

The story I told in the last post is not over. The recent development is that we spotted a mistake in the paper. An easy mistake to make: we had simply used the symbol n in two different places with … Continue reading →

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Synchronization and separation in the Johnson schemes

Posted on 06/06/2017 by Peter Cameron

Today a paper by Mohammed Aljohani, John Bamberg and me went on the arXiv on this topic. Here is a brief summary of what it is about. Synchronization comes in several flavours, and the point of the paper is to … Continue reading →

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More graphs

Posted on 25/05/2016 by Peter Cameron

John Bamberg is reporting on New Directions in Combinatorics on SymOmega (his report on Day 1 is here), so I will not even attempt to be comprehensive, but will just pick some plums. Not very long ago, I reported the … Continue reading →

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Terminology: association scheme or coherent configuration?

Posted on 08/06/2014 by Peter Cameron

At the Villanova conference, many of the talks were about association schemes or coherent configurations, or indeed generalisations of these. A certain tension between different uses of these terms was evident. I’d like to set down my own views here. … Continue reading →

Posted in exposition, history | Tagged , , , , , , , , , , | 2 Comments

Multiply transitive permutation sets

Posted on 08/04/2012 by Peter Cameron

Bill Fahle asked, in a comment on the preceding post, for information about sets of permutations which are multiply transitive (but not necessarily groups or sharply multiply transitive). I take “t-transitive set” to mean a set S of permutations of … Continue reading →

Posted in exposition | Tagged , | 10 Comments

Coherent configurations and all that, 1

Posted on 30/03/2012 by Peter Cameron

I’m off to Lisbon next week for three weeks. Among other things, I will be giving four lectures at the Centre for Algebra at the University of Lisbon. One of these will touch on aspects of association schemes and coherent … Continue reading →

Posted in exposition, history | Tagged , , , | 9 Comments